As a novel functional monosaccharide, L-arabinose is one type of important pharmaceutical intermediates, which is widely used in the synthesis of anticancer, antiviral and cardiovascular medicines such as cytarabine and L-ribose. It can also be used in biochemistry for preparation of culture medium and spices and so on. In addition, it has been discovered in recent year that L-arabinose has an excellent property of inhibiting the increase of glucose concentration in serum by inhibiting sucrose absorption noncompetitively. Thus it can prevent and treat obesity and hyperglycemia, showing a great market potential in weight loss and control of diabetes. L-arabinose has been approved as health food supplements by Food and Drug Administration (FDA) and The Japanese Ministry of Health, and it is also regarded as anti-obesity agents and nonprescription drugs by American Medical Association. So L-arabinose has wide prospect in medicine and food industries.
In nature, L-arabinose exists in fruit purees, hemicellulose, and pectate in the form of polysaccharide araban, L-araboxylan, L-arabinogalactan. Nowadays, the main industrial process for L-arabinose production still relies on extraction and purification using natural gum arabic as feedstock. Prior to the present invention, as introduced in relevant literatures, there are following methods for preparing L-arabinose from gum arabic.
The patent publication with the publication number of CN102146102A describes a method of preparing L-arabinose and D-galactose through hydrolysis of gum arabic with acid, then neutralization with aqueous alkali followed by evaporation. The mixture is then converted to the corresponding acetone acetals by ketone. It is selectively extracted with alcohol and finally deacetalize to obtain L-arabinose and D-galactose, with the yield as high as 15%˜24% of material weight. Though L-arabinose and D-galactose can be obtained simultaneously, the process requires relatively large amounts of organic solvents and pollutes environment seriously.
It is not environmentally friendly, moreover, product purity is still far below standard. S. Mukher Jee and A. N. S Shrivastava used arabic Sundra gum as the raw material to obtain L-arabinose, D-galactose and rhamnose by means of hydrolysis followed by column chromatography with a large amount of half-saturated butanol aqueous solution (J Sci. Ind. Research India, 1956, 168, 566-7).
The patent publication with the publication number of CN1373135A describes a method of extraction of L-arabinose from Gum Arabic by chromatographic separation on two columns. Gum arabic is hydrolyzed with a mineral acid solution to yield the mixed solution followed by neutralization with alkali, which was concentrated and extracted with alcohol and then precipitated by quadruple amount of acetic acid. L-arabinose can be obtained further by chromatographic separation using n-butanol, ethyl acetate, iso-butanol, acetic acid as eluents. The purity of L-arabinose is 96%˜99.5% and the yield is 16%˜18%.
Patent EP0115068 describes a process for the production of L-arabinose from arabic PYCNANTHA gum. The process includes hydrolyzing gum with acids followed by neutralizing with IR-4B(OH) anion resin, and extracting with ethanol. L-arabinose and its derivatives can be obtained by column chromatography with a large amount of half-saturated ethyl acetate solution.
In summary, all forementioned purification methods require a great amount of organic solvents, resulting in large energy consumption and high cost. There are still some difficulties for these processes to be adopted for practical industrial production.
The patent publication with the publication number of CN102146102A proposes a different method for L-arabinose production. The gum arabic was firstly decomposed by enzyme, which is produced from a highly selective strain of Fusarium sp. The degradation mixture was then purified by traditional separation methods. The high-purity L-arabinose can be obtained with the recovery as 18% of material weight. The advantages of this method include mild reaction conditions and low dissipation of equipment. However, the process is still difficult to be industrialized because of inefficient hydrolysis and rigid operation conditions.